sedimentary

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale. Color: Brown, tan, and reddish-orange due to iron oxides. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None, exhibits conchoidal (shell-like) fracture.

Hardness: 7 on Mohs scale
Color: Brown, tan, and reddish-orange due to iron oxides
Luster: Dull to waxy

Identified April 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or through chemical precipitation in sedimentary environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in road construction as aggregate and occasionally as semi-precious gemstones for jewelry (Jasper/Agate).

Geological facts

Chert was one of the most important minerals for early humans because of its ability to be knapped into sharp tools. It is also used as a fire-starter when struck against steel to create sparks.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel) and its smooth, curved conchoidal fractures. Commonly found in riverbeds, glacial till, and limestone outcrops globally.

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